Power systems have been devised which include a steam generator in constantly open fluid communication with the expansible chamber of a cyclically operable engine. The engine generally is of the type having a rotor or piston which forms a movable wall of the chamber. A noncombustible vaporizable liquid, such as water, is injected into the heated generator during a portion of the engine cycle. In the case of those having a reciprocating piston, injecting the liquid usually begins just prior to the piston reaching top dead center. Steam is generated, pressurizing the chamber, to compel the piston into a power stroke. Injecting is stopped at some point during the power stroke. Means are provided to partially or fully exhaust the chamber and to return the piston, wherein the process is repeated.
This type of apparatus obviates the need for a steam inlet valve, but requires an inlet valve for the vaporizable liquid. An advantage of the valve swap is that it rids the system of a source of energy loss. For example, a liquid inlet valve orifice is much smaller than that of a steam inlet valve serving an expansible chamber of similar size. Therefore, much less force is required to open the liquid inlet valve than that of the steam inlet valve under high operational pressure. The force difference, in many cases, is in the order of hundreds of times.
Another advantage of the apparatus that no more steam is generated than the amount needed during a power stroke. This greatly reduces the hazard if the generator is accidentally ruptured; an important safety consideration for automotive use.
One of the simplest embodiments of an apparatus of the type described includes a hollow engine cylinder head. The cylinder head encloses one end of a cylinder such that the interior chamber of the head is in open fluid communication with an expansible chamber within the cylinder. Typically, the head is heated by means including a heating fluid passing through a jacket encircling the head chamber. An injector is disposed to inject the expansible liquid into the head chamber at intervals cyclically timed as described hereinbefore. However, the amount of energy that can be rapidly transferred from the heating fluid to generate and heat the steam is minimized by the lack of sufficient heat exchange surface within the head.
Other, more complex generators include parallel spaced fins, vanes, or the like, as heat exchange surfaces. However, the time required to transfer thermal energy longitudinally along fins, or vanes, results in a sluggish response to changing conditions; changes required for control purposes, for example.
The surfaces of tubes have also been used for heat exchanging in such generators. But, a quantity of tubes or tubing, as with fins or vanes, presents a heretofore unresolved problem of distributing a fine spray of vaporizable liquid directly onto a large total surface area in a relatively small steam generating chamber. Loops of tubing, layers of tubes, or layers of fins or vanes, tend to impede the sprayed liquid from directly contacting all the surfaces of respective adjacent loops or layers.
Suspended droplets of the liquid will flash into steam without surface contact if their temperature is sufficient for the given pressure. When this occurs, the pressure rises and more energy is required for vaporization of more droplets to continue the process. Additional droplets in the same environment could be vaporized, within the time constraints of the engine power stroke, by absorbing energy from direct contact with an appropriate heat exchanging surface.